Plural lamp ballast



Sept. 29, 1964 v. w. oLsoN PLURAL LAMP BALLAST Filed July 12. 1960FII-5.5

NKJUX Jang United States Patent() 3,151,276 PLURAL LAMP BALLAST VictorW. lson, Chicago, lll., assigorto Jefferson Electric Company, Bellwood,lili., a corporation of Delaware Filed .luly 12, 1960, Ser. No. 42,285 7Claims. (Cl. 315-231) This invention relates to a plural lamp ballastfor are discharge devices.

The plural lamp ballasts heretofore used have been either a series typeor a lead-lag type. In the series type, if one lamp is extinguished, theother lamp is necessarily extinguished. In the lead-lag type if one lampis extinguished, the other will remain in operation, but the powerfactor of the ballast is very poor.

It is an object of the present invention to provide a plural lampballast in which the various lamps are connected in parallel across theballast, and in which the arrangement is such that one or more of thelamps will operate satisfactorily even after one or more of the otherlamps have been extinguished or removed.

Due to the unstable characteristics of gaseous discharge devices it hasheretofore been though necessary to provide a separate inductance ineach branch of a parallel lamp circuit, in order to provide forindependent lamp operation.

According to the present invention, I have found that a commoninductance can be provided for all branches, and still obtainindependent lamp operation.

In general, if a separate capacitance is provided for each branchcircuit, and if the common inductance is nonlinear, I have found thatwhen one or more lamps are removed, the ballast will stabilize itself ata somewhat lesser secondary voltage, and provide regulated operationthereafter for the remaining lamps.

Thus it is possible to obtain considerable savings in the manufactureand installation of plural lamp lixtures because only on transformer isrequired for each group of two, three or four or more lamps.

Another object is to provide in a plural lamp ballast of the characterdescribed, an arrangement which deliverssubstantially constant wattageto each of the lamps irrespective of quite substantial variations inline voltage, andirrespective of variations in the voltage delivered toeach branch circuit.

For instance when several ballasts are connected in parallel across aline, it frequently happens that the line yvoltage for the end ballastis considerably less than the line voltage for the iirst ballast, due toline loss. According to my invention this does not affect the wattage orlight output of the lamps energized from the last ballast. Similarly, ininstances where several lamps are energized from a common ballast andare located at varying distances therefrom, the voltage available forthe last lamp may be somewhat less than that available for the others,but according to the present invention, the wattage of all lamps will beapproximately the same.

The invention is described herein as applied to mercury vapor lamps suchas those used for street lights, however, it will be understood that theinvention is applicable to ballast for other types of gaseous dischargedevices such as the ordinary lluorescent lamp.

Other objects, features and advantages will become apparent as thedescription proceeds.

With reference now to the drawings in which like reference numeralsdesignate like parts:

FIG. l is an elevation of the core structure of a preferred embodimentof my invention, the windings being shown in dotted lines;

FIG. 2 is an electrical diagram of the ballast;

3,151, PatentedV Sept. 29, 1964 ICC FIG. 3 is a graph illustrating theoperating range of my invention; and

FIG. 4 is a graph illustrating the constant wattage char acteristic ofmy improved ballast.

With reference now to FIG. 1, the ballast includes a high reactancetransformer 10 having a primary winding 11 and a secondary winding 12.The windings 11 and 12 are mounted in end to end relationship on awinding leg 13 so as to provide a linx leakage path therebetween.

In the embodiment shown, the leakage path is of comparatively lowreluctance due to the provision of magnetic shunt portions 14 on thewinding leg.

The core structure may be of any desired construction; as shown in FIG.l it is a shell type pressed lit core which includes the winding leg 13and a yoke 15. The yoke is also provided with shunt portions 16 whichare separated from the shunt portions 14 by an air gap 17.

The core structure is designed to operate at saturation which fact isindicated diagrammatically in FIG. 1 by showing the width of the windingleg as being somewhat less than the sum of the widths of the yokeportions. However, it will be understood that saturation is a functionof core cross section with respect to ampere turns and that the coreparts, if desired, may be of the customary proportions in which thewidth of each yoke leg is oneehalf the width of the winding leg.

As shown in FIG. 2, the primary winding 11 is connected to a line 20.Leads 21 and 22 extend from the secondary winding 12. The secondarycircuit includes two or more branches. The first branch circuitcomprises a condenser 23 and a lamp 24, such as a 400 watt mercury vaporlamp type H-l or H-33. The second branch circuit comprises a condenser25 and a lamp 2.6. Cther branch circuits may be provided as indicated bythe condensers 27, 29 and lamps 28, 3l) shown in dotted lines, althoughthe specific example described below applies only to the parts shown insolid lines.

The characteristic of my invention is that when the ballast is designedfor two lamp operation, as indicated by the solid line circuit of FIG.2, if one of the lamps 24 or 26 is removed, the remaining lamp willcontinue in operation, at a somewhat reduced wattage. The same appliesif one of the lamps is broken or becomes inopera- -tive for any reason.

When the ballast is designed to operate three lamps, if one lamp isremoved the other two remain in operation. Similarly the circuit may bedesigned -to operate four or six or an` even greater number of lamps,and in general up to half of the lamps may be removed, and the remaininglamps will continue in stable operation.

In general, this result is obtained by designing the transformer 10 witha relatively small number of turns so that the secondary winding 12 willdraw a magnetizing current which is high with respect to the loadcurrent. The cross section of the core structure, or at least of thewinding leg 13, is relatively low with respect to the magnetizingcurrent so that the transformer operates at saturation.

As a rough design parameter, the magnetizing current of the secondarywinding at operating voltage should be substantially 50% to 75% of thefull load current. This is determined by a primary open circuit test inwhich the voltage applied to the secondary is the same as the secondaryvoltage when operating under full load.

The curve of 31 of FIG. 3 represents the violtage-eurrent characteristicof the secondary winding as the line voltage is increased from zero upto and through the normal operating range. The flattened portion 31a ofthe curve which extends from I1 to I2 represents the desired range ofoperation. For instance, in the design of a four lamp ballast, thetransformer would be wound so that the full load current would occur atabout the point where the 33 curve 31 intersects the abscissa I2, and sothat the current drawn by only two lamps would be that which would occurwhere the curve 31 intersects the abscissa I1. Thus it will be seen thateven though the current is reduced by 50%, the voltage across thesecondary leads 21 and 22 is maintained within the operating range ofthe lamps.

As a specific example, a transformer was constructed having a core asshown in FIG. 1. The winding leg 13 was 1.25 inches in width, and eachof the yoke legs was .S75 inch in width. The overall dimensions of theyoke 15 were 5.75 inches square, and the other parts were dimensioned inthe proportions shown in FIG. l. The magnetic shunts 14 and 16 were .625inch wide, and the gap 17 was .050 inch long.

The laminations were stamped from M19 grade (A.I.S.I. type) 26 gaugesteel. The lamination stack was 3.75 inches high.

The primary winding 11 contained 98 turns of number 11 wire (A.W.G.) andthe secondary winding 12 contained 200 turns of number ll wire. Thisturn ratio provided suiiicient o-pen circuit voltage to strike thelamps.

The condensersr23 and 25 were 31.0 mfd. each, or in the alternative, two15.7 mfd. condensers were used in parallel. The lamps were 400 wattI-I-l mercury Vapor lamps.

When the two lamp system was energized by connecting the primary 11 to a115 volt line; the primary ilux density was substantially 110,000 linesper square inch and the secondary Eux density was substantially 130,000lines per square inch.

During operation, the crest factor of the lamp current was less than1.7, and regulation was better than 1%, meaning that a plus or minus 13change in line voltage resulted in a change of less than plus or minus1% in the wattage across the lamp.

During both two lamp operation and single lamp operation at 115 lineVoltage, the voltage drops across the various circuit elements, and thecurrent traversing the same, are set forth below:

is to say, when all of the lamps are operating. In the above tabulationshown, it will be observed that under two lamp operation, the voltagedrop across the condenser Xc is almost twice the voltage drop across thelamp. This relationship is believed to contribute materially totheapparent constant impedance of the branch circuit above referred to. v

Variations in the condenser size may require slight variations in thelength of the air gap 17. However, for the particular type of circuitshown, I have found that the air gap should be relatively small, of theorder from .030 inch to .080 inch, the longer gap being associated witha small condenser size, and vice versa.

Furthermore, with respect to each of the several conditions ofoperation, such as all lamps in circuit, one lamp removed, two lampsremoved, etc., the system provides relatively constant lamp wattage withrespect to line voltage variation. This constant wattage characteristicis shown in the graph of FIG. 4, in which the vertical axis representspercentage variation in Watts delivered to a given lamp, and in whichthe horizontal represents line voltage, normal voltage being 115 volts.Curve 32 indicates lamp wattage under two lamp operation, and curve 33represents lamp wattage under one lamp operation, in the circuit of FIG.2.

Although only a preferred embodiment of my invention has been shown anddescribed herein, it will be understood that various modifications andchanges may be made therein without departing from the spirit of myinvention as pointed out in the appended claims.

I claim:

1. A plural lamp ballast comprising a leakage reactance transformerhaving a core including a Winding leg, a primary winding and a secondarywinding located on said winding leg in end to end relationship toprovide a flux leakage path, the cross sectional area of a substantialportion of that part of said core which is linked by said secondarywinding being suiciently small so that said transformer will operate atsaturation, lead means Primary Secondary Branch I. Watts RF., V. 1. YX., Lamp I. Lamp percent Watts 1 Two lamp operation. 3 Open circuit.

The foregoing tabulation shows that in the circuit 2 Single lampoperation.

for connecting said primary winding to a source of A.C.

shown, the impedance of the transformer 10, instead of causing anincrease in the secondary voltage as the load is reduced, cooperateswith the other circuit elements so that the voltage across the secondaryterminals is reduced as the lamps are removed one by one.

Furthermore, with respect to each branch circuit, the combination of thecondenser in the branch circuit and the inductance in the transformernot only provides stable ballasting for each lamp, but due to thesaturation, a very desirable type of regulation is provided in which adecrease in the secondary voltage due to removal of a lamp results in amuch smaller decrease in the voltage across the remaining lamp or lamps.

Actually, in the two lamp ballast shown, the decrease in the branchcircuit current is roughly proportional to the decrease in the secondaryVoltage which suggests that the impedance of the branch circuit remainssubstantially constant, although due to changes in wave shape, it is notpossible to speak unequivocally.

However, I have found, especially with respect to the ballasting ofmercury vapor lamps, that stable operation can be obtained, in spite ofa change in the secondary voltage of as much as 10 to 15%, if theimpedance of the condenser is considerably in excess of the impedance ofthe lamp under full load conditions of the ballast, which voltage and aplurality of branch circuits connected in Yparallel across saidsecondary, each of said branch circuits including a condenser and leadmeans for connection to a gaseous discharge device for energizing same,whereby removal of a gaseous discharge device from its branch circuitwill render said branch circuit inoperative so that both the loadcurrent and the capacitive reactance of the load will be reduced,resulting in a decrease in the voltage across said secondary winding,the saturation of said core causing said resulting decrease in secondaryvoltage to be much smaller proportionately than said reduction in loadcurrent.

2. A plural lamp ballast as claimed in claim 1 in which the impedance ofsaid condenser is approximately twice the impedance of said lamp whensaid ballast is operated at full load current.

3. A plural lamp ballast as claimed in claim 1 having a gapped magneticshunt interposed between said primary and secondary windings to reducethe reluctance of said ux leakage path.

4. A plural lamp ballast as claimed in claim 3 in which the gap of saidmagnetic shunt is from .030 to .080 inch in length.

5. A plural lamp ballast as claimed in claim 1 in Which the inductanceof said secondary winding is suiiiciently U small that when a voltage isapplied to the terminals thereof of a magnitude equal to the normaloperating voltage, the current drawn by said secondary winding when saidprimary winding is open circuited will be from substantially 50% to 75%of the full load current during normal operation.

6. A lighting system comprising a leakage reactance transformer having acore structure, a primary winding and a secondary Winding mounted onsaid core structure in spaced relationship to provide a flux leakagepath therebetween, a source of A.C. voltage connected to said primaryWinding and a plurality of branch circuits connected in parallel acrosssaid secondary, each of said branch circuits including a condenser and agaseous discharge device, whereby removal of a gaseous discharge devicefrom its branch circuit will render said branch circuit inoperative sothat both the load current and the capacitive reactance of the load willbe reduced, resulting in a decrease in the Voltage across said secondarywinding, the impedance of said condensers being substantially greaterthan the impedance of said lamps under normal operating conditions,whereby a remaining branch circuit will stabilize itself for continuedoperation at said reduced secondary voltage.

7. In combination, a leakage reactance transformer adapted forenergizing a plurality of gaseous discharge devices in parallel, saidtransformer having a core including a winding leg, a primary winding anda secondary winding mounted on said winding leg in end to endrelationship, a magnetic shunt disposed between said Windings, a sourceof A.C. voltage connected to said primary winding, a plurality ofgaseous discharge devices, and a plurality of condensers connected inparallel across said secondary, each condenser being connected in seriesto a gaseous discharge device, said secondary winding being constructedto draw a magnetizing current which is relatively high with respect tothe normal load current of said secondary, and said normal load currentbeing sufficiently high as to saturate the secondary portion of saidwinding leg.

Wiegand July 23, 1935 Feinberg June 22, 1954

1. A PLURAL LAMP BALLAST COMPRISING A LEAKAGE REACTANCE TRANSFORMERHAVING A CORE INCLUDING A WINDING LEG, A PRIMARY WINDING AND A SECONDARYWINDING LOCATED ON SAID WINDING LEG IN END TO END RELATIONSHIP TOPROVIDE A FLUX LEAKAGE PATH, THE CROSS SECTIONAL AREA OF A SUBSTANTIALPORTION OF THAT PART OF SAID CORE WHICH IS LINKED BY SAID SECONDARYWINDING BEING SUFFICIENTLY SMALL SO THAT SAID TRANSFORMER WILL OPERATEAT SATURATION, LEAD MEANS FOR CONNECTING SAID PRIMARY WINDING TO ASOURCE OF A.C. VOLTAGE AND A PLURALITY OF BRANCH CIRCUITS CONNECTED INPARALLEL ACROSS SAID SECONDARY, EACH OF SAID BRANCH CIRCUITS INCLUDING ACONDENSER AND LEAD MEANS FOR CONNECTION TO A GASEOUS DISCHARGE DEVICEFOR ENERGIZING SAME, WHEREBY REMOVAL OF A GASEOUS DISCHARGE DEVICE FROMITS BRANCH CIRCUIT WILL RENDER SAID BRANCH CIRCUIT INOPERATIVE SO THATBOTH THE LOAD CURRENT AND THE CAPACITIVE REACTANCE OF THE LOAD WILL BEREDUCED, RESULTING IN A DECREASE IN THE VOLTAGE ACROSS SAID SECONDARYWINDING, THE SATURATION OF SAID CORE CAUSING SAID RESULTING DECREASE INSECONDARY VOLTAGE TO BE MUCH SMALLER PROPORTIONATELY THAN SAID REDUCTIONIN LOAD CURRENT.